1. Field of Invention
The present invention relates to a signaling framework for supporting mobile terminals in a wireless asynchronous transfer mode (ATM) network. Specifically, the invention refers to control protocols for handoff between base stations and mobile terminals.
2. Background and Description of Related Art
The rapid worldwide growth of digital wireless communication services has led to a new generation of mobile switching networks to serve as infrastructure for such services. Given the wide range of radio access technologies being employed for both telephone and Internet access, new mobile switching architectures are needed to provide generic, cost-effective support for a variety of cellular and wireless data technologies. In addition, mobile networks being deployed in the near future should be capable of smooth migration to future broadband services based on high-speed wireless access technologies, such as wireless ATM.
The basic idea of wireless ATM is to use a standard ATM cell for network level functions, while adding a wireless header/trailer on the radio link for wireless channel specific protocol sublayers (medium access control, data link control and wireless network control). ATM virtual circuits with quality of service control are supported on an end-to-end basis via standard ATM signalling functions which are terminated at the mobile unit. Terminal migration related functions such as handoff control and location management are handled by suitable mobility support extensions to ATM signalling/control protocols implemented at the radio port (base station) and switches within the fixed network.
A mobile ATM network offers several advantages over non-ATM networks. One advantage is that it provides a high-speed backbone network that provides a common infrastructure network to a diverse set of mobile technologies. A second advantage is that it offers mobility support to terminals, independent of the wireless access technology.
A basic architecture for wireless ATM networks in which broadband services are extended over shared radio channels, and which incorporates suitable medium access control and data link control layers into the standard ATM protocol stack, was proposed by D. Raychaudhuri and N. Wilson in an article entitled, ATM Based Transport Architecture for Multiservice Wireless Personal Communication Network, IEEE JSAC, October 1994. Additional information on mobile ATM networks was disclosed by D. Raychaudhuri in an article entitled, Wireless ATM Networks: Architecture, Systems Design and Prototyping, IEEE Personal Communications, August 1996. Both articles are incorporated herein by reference.
A wireless ATM system broadly consists of a radio access layer and a mobile ATM network. The radio access layer consists of several new protocol sublayers necessary to extend ATM services over a wireless link. The major functions of this layer include high-speed physical level transmission/reception, medium access control for channel sharing by multiple terminals, data link control for amelioration of radio channel impairments, and wireless control for radio resource management and metasignaling.
Mobile ATM is the term used to denote the set of enhancements needed to support terminal mobility within a fixed ATM network. The major functions of mobile ATM are location management, for mapping of user names to their current locations, and handoff control, for dynamic rerouting of virtual channels during terminal migration. Note that mobile ATM is intended to be independent of the specific radio access technology used. This means that in addition to supporting end-to-end wireless ATM services via the radio access layer, mobile ATM capabilities can be used to provide an interconnection infrastructure for existing personal communications systems (PCS), cellular and wireless LAN applications.
Medium access control is the subject of U.S. Pat. No. 5,638,371, entitled "Multiservices Medium Access Control Protocol for Wireless ATM System." Data link control is the subject of U.S. patent application Ser. No. 08/553,168, entitled "Data Link Protocols for Wireless ATM Access Channels." Handoff control is the subject of U.S. patent application Ser. No. 08/773,738, entitled "Handoff-Control Technique for Wireless ATM." The patent and two applications are assigned to the same assignee as the present invention and are all incorporated herein by reference.
One of the problems with the current design of mobile ATM networks is that data cells being transmitted to and from a mobile terminal can sometimes become lost, duplicated or placed out of order when the mobile terminal is handed off from one base station to another. Several aspects of this issue have been addressed in an article by H. Mitts et al., entitled "Lossless handover for wireless ATM, ACM/Baltzer Mobile Networks and Applications, December 1996 and an article by M. Ajome Marsan, et al., entitled "Buffer Requirements for Loss-Free Handovers in Wireless ATM Networks, Proceedings of the 3rd IEEE ATM Workshop, May 1997.
The present invention provides a method whereby connections from a mobile terminal can be seamlessly re-rerouted from one base station to another without data loss, duplication or misordering of data.